1. Field of the Invention
The present invention relates to a process of preparing a metal ion imprinted polymer that can separate heavy metal ions selectively.
2. Background Art
A molecularly imprinted polymer (MIP) or metal ion imprinted polymer (MIIP) as an eco-friendly and simplified separation tool has been developed. The term MIP or MIIP is referred to as the polymer which includes a space of the same form as a template. The space is formed by removing a template after a polymer is synthesized using as starting material a monomer bonded with the template.
Since only the template can be inserted into the space and a molecule whose stereo-structure is different from that of the template cannot be inserted, other molecules that are different from the template in structure can be separated using the polymer having the template space. This is the same theory as Fischer's Lock-and-Key Concept in which an antibody specifically interacts with a corresponding antigen, or Receptor Theory in which an enzyme has a specific activity with its counterpart substrate.
A process for preparing an MIP is disclosed in EP0190228. More specifically, to prepare an MIP or MIIP, a template is dissolved in a porogen and the template is mixed with a polymerizable monomer having a functional group that can react with a part of the template. Thereafter, polymerization is started by adding an excessive amount of a polymerization initiator and a cross-linker (i.e., an inert monomer) to maintain the array of functional monomers bonded with the template. In this procedure, the porogen dissolving the template plays an important role to determine the properties of the synthesized polymer. Particularly, since a polar porogen dissolves polar molecules, the bonds between the template and functional single molecules can be destroyed.
Actually, in connection with MIP techniques, numerous researches have been carried out to design and prepare molecules capable of recognizing specific molecules. Most of the researches have focused on separation of compounds difficult to be separated, for example, racemic mixtures, amino acids and so on.
The basic idea of the molecularly imprinted polymer technique to be applied to selective separation of heavy metal ions was suggested very recently. Researches have been performed in some developed countries such as the United States, Japan, Sweden and so on and the scope of the researches is becoming wider.
The Mosbach group of Lund University in Sweden tried selective separation of some kinds of similarly structured compounds by ion imprint [Mosbach, K. Trends biochem. 19, 9 (1994)]. Thereafter, the Murray group of Maryland University suggested the possibility of applying the selective separation property to metal ions like Pb(II), Cd(II), Li(I), Na(I), Mg(II), Ca(II), Cu(II), Zn(II), Hg(II) and so forth [Rrasado Rao, T., Sobhi Daniel, Mary Gladis, J., Trends in Analytical Chemistry, 23, 28 (2004), Yongwen Liu, Xijun Chang, Sui Wang, Yong Guo, Bingjun Din, Shuangming Meng, Analytica Chimica Acta, 519, 173 (2004)]. In addition, the Fish group of Lawrence Berkley Laboratory confirmed selective separation of Zn(II) ions using triazacyclononane ligand. Also, Japanese researchers including Kyushu University have made efforts to develop new separation tools using metal ion imprint with some significant results achieved.
When preparing the imprinted polymer using emulsion or suspension polymerization, however, attraction acting between the functional group of the monomer or template and water is required to be prevented. One suggested method is to use, in place of water, a dispersion solvent, which is not mixed with an organic monomer in emulsion polymerization and has no mutual attraction to the template. Since liquid perfluorocarbon is not mixed with most of the organic compounds, it can be used as a dispersion solvent in solution polymerization. In polymerization, liquid perfluorocarbon is expected to be able to emulsify the monomer, cross-linker, template, porogenic solvent and so on stably by interface activity of the fluoro series. Further, since there is no attraction acting on the functional group of the monomer and the solvent used in the polymerization, the number and the force of the conceiving (recognition) position are believed to be hardly affected [U.S. Pat. Nos. 5,872,198 and 5,959,050].
Nonetheless, liquid perfluorocarbon is expensive and the manufacturing costs for industrial application are high.
Accordingly, there is thus a need for a new process of preparing a metal ion imprinted polymer without using liquid perfluorocarbon.